JP6945930B2 - Method for separating selenium and tellurium dissolved in molten chloride - Google Patents

Description

The present invention relates to a method for separating selenium (Se) and tellurium (Te) dissolved in molten chloride from the molten chloride.

For example, FIG. 16 shows an outline of the process of electrolytically reducing an oxide fuel in molten chloride such as LiCl or CaCl _2. When the oxide fuel is electrolytically reduced in the molten chloride, the oxide fuel loaded on the cathode is reduced to a metal, and oxygen is eluted / dissolved in the molten chloride. On the other hand, oxygen gas is released from the anode.

The chemical reaction formulas that proceed at the cathode and anode in the electrolytic reduction process are shown below. In the following chemical reaction formula (A), X is uranium (U), plutonium (Pu), or minor actinide (MA).
^{_{Cathode: XO 2 + 4e - → X}} + 2O 2- ··· (A)
_{^{Anode: 2O 2- → O 2 + 4e}} - ··· (B)

In the above electrolytic reduction process, some fission products are also eluted / dissolved into the molten chloride. Fission products that elute / dissolve into molten chloride contain selenium and tellurium, which dissolve in molten chloride in the form of ^{anions (ie, Se 2-} , Te ^2-). There is.

Here, selenium is a radioactive substance having a long half-life, and it is desirable to separate it from other substances and treat or store it separately while ensuring safety. Further, in the above-mentioned electrolytic reduction process, if tellurium accumulates in the molten chloride, it may eventually precipitate as an electrically insulating tellurium oxide on the anode and interfere with the electrolysis. Therefore, selenium and tellurium dissolved in the molten chloride need to be separated and recovered from the molten chloride.

However, there are few reports that directly show that selenium and tellurium are separated and recovered from molten halides such as molten chloride. If the prior art is dared to be mentioned, Non-Patent Document 1 describes molten chloride, which is considered to hinder the continuation of regenerative electrolysis by performing electrolysis using copper as an anode in the regenerative electrolysis process of lithium (Li) in molten chloride. It has been shown that tellurium in an object _{is deposited as Cu 2} Te on the surface of the anode and removed.

Electric Power Central Research Institute "Development of Oxide Fuel Reduction Technology", Electric Power Central Research Institute Report T03062, 2004

However, when the method described in Non-Patent Document 1 is applied to the separation / recovery of tellurium from molten chloride, since electrolysis is performed, complicated operations such as preparation of electrodes and power supply and voltage control are required. Become. Moreover, _{the rate at which Cu 2} Te precipitates on the surface of the anode is extremely slow, and it takes a long time for separation and recovery. Therefore, the separation / recovery method using electrolysis has a problem of lacking practicality.

Therefore, an object of the present invention is to provide a method capable of easily separating selenium and tellurium from the molten chloride without performing electrolysis, and further efficiently and quickly. ..

As a result of diligent studies by the inventor in order to achieve this purpose, selenium dissolved in the molten chloride _{is reacted with a metal oxide such as copper oxide (Cu 2} O) or nickel oxide (Ni O). It was found that it is possible to separate and recover from the molten chloride by using a selenium metal such as Cu ₂ Se or Ni ₃ Se _2.

That is, it was found that selenium dissolved in the molten chloride can be separated by utilizing a chemical reaction which is considered to be more advantageous than electrolysis, especially from the viewpoint of treatment speed.

This finding was also considered to apply to tellurium, which is an element of the same family as selenium and has similar chemical properties.

Based on this finding, the inventor has made various further studies to complete the present invention.

Specifically, selenium and method for separating tellurium dissolved in molten chlorides of the present invention, the metal is formed by Cu to Cu ₂ O in storage container with loading into the container a Cu ₂ O member Is inserted, and the storage container in which the metal member formed of the Cu is inserted is immersed in the molten chloride, and at least of selenium (Se) and tellurium (Te) dissolved in the molten chloride. One of them is reacted with Cu ₂ O to be separated from the molten chloride as a selenium metal or a tellurized metal.
Further, the method for separating selenium and tellurium dissolved in the molten chloride of the present invention is formed by loading NiO into a storage container and inserting a metal member formed of Ni into NiO in the storage container to form Ni. The storage container in which the metal member is inserted is immersed in molten chloride, and at least one of selenium (Se) and tellurium (Te) dissolved in the molten chloride is reacted with NiO. It is characterized by being separated from the molten chloride as a selenium metal or tellurium metal.

Therefore, according to this method, selenium and tellurium are separated / recovered from the molten chloride by a simple method of contacting the molten chloride with Cu ₂ O or Ni O without performing electrolysis.

The method for separating selenium and tellurium dissolved in the molten chloride of the present invention may be such that Cu ₂ O or Ni O is a powder. In this case, the contact area with the increased specific surface area of Cu ₂ O or NiO Cu ₂ O or NiO and molten chlorides increases.

The method for separating selenium and tellurium dissolved in the molten chloride of the present invention may be carried out at least one of stirring the molten chloride and moving the container in the molten chloride. .. In this case, the occurrence of bias depending on the concentration of selenium or tellurium in the molten chloride is avoided, and the reaction efficiency / reaction rate of selenium or tellurium dissolved in the molten chloride and Cu ₂ O or NiO is avoided. Is maintained.

The method for separating selenium and tellurium dissolved in the molten chloride of the present invention is such that the molten chloride is a lithium chloride (LiCl) -potassium chloride (KCl) eutectic salt or a calcium chloride (CaCl ₂ ) molten salt. Is also good. In this case, efficient production of selenium metal and tellurium metal is appropriately performed.

According to the present invention, selenium or tellurium can be obtained from the molten chloride by a simple method of contacting the molten chloride with a metal oxide (Cu ₂ O or Ni O) composed of the metal M (Cu or Ni). It can be separated / recovered. Therefore, it is possible to easily separate / recover selenium and tellurium from the molten chloride without performing complicated operations such as preparation of electrodes and power sources and voltage control as in the case of electrolysis. Moreover, since the separated forms of selenium dioxide and telluride metal are stable compounds even in high-temperature molten chloride, selenium alone (boiling point of 685 ° C.), tellurium alone (boiling point of 990 ° C.) or volatilization with high vapor pressure Compared with the case where selenium dioxide (SeO ₂ , sublimation temperature 317 ° C.) or the like is used as a separation / recovery form, it has an advantage that it is easy to handle in high-temperature molten chloride and it is easy to separate / recover.

According to the present invention, further, when Cu ₂ O or Ni O is simply placed in a storage container and immersed in molten chloride, the interface between Cu ₂ O or Ni O and the molten chloride (in other words, the storage container). while Cu ₂ O or reacts only with the upper surface) of the NiO of the inner is only happen, the Cu ₂ O or reservoir portion of NiO in storage container to insert the metallic members formed of Cu or Ni By doing so, the surface of the metal member made of Cu or Ni exposed in the molten chloride also acts as a reaction surface, so that the reaction can proceed efficiently and the separation / recovery of selenium and tellurium can be promoted. There is also a metal oxide (Cu ₂ O or NiO) composed of metal M (Cu or Ni) and a selenium metal or a tellurized metal, and the ratio of M / O to M / Se, M / Te is Since the composition is adjusted by M supplied from a metal member formed of Cu or Ni in different cases, the reaction can proceed appropriately, and the raw material Cu ₂ O or Ni O and the product (that is, the product). , Serene, telluride) can be efficiently separated / recovered from the molten chloride without being dispersed / dispersed in the molten chloride.

The present invention, when the Cu ₂ O or NiO has to be a powder, thereby to increase the specific surface area of Cu ₂ O or NiO increases the contact area with the Cu ₂ O or NiO and molten chlorides It is possible to increase the reaction rate of Cu ₂ O or Ni O with selenium or tellurium dissolved in the molten chloride to rapidly produce a metallized metal or a tellurized metal. Therefore, the time required for the reaction / separation treatment can be shortened, and the time required for separation / recovery of selenium and tellurium from the molten chloride can be shortened.

In the present invention, when the molten chloride is agitated or the storage container is moved in the molten chloride, the reaction between selenium or tellurium dissolved in the molten chloride and Cu ₂ O or NiO The efficiency and reaction rate can be maintained, and selenium metallized metal and tellurium metallized metal can be rapidly produced. Therefore, the time required for the reaction / separation treatment can be shortened, and the time required for separation / recovery of selenium and tellurium from the molten chloride can be shortened.

The present invention is molten when the chloride is or to be a LiCl-KCl eutectic or CaCl ₂ molten salt can be appropriately performed efficiently generate selenide metal or metal telluride, It will be possible to reliably promote the separation / recovery of selenium and tellurium.

It is a process schematic diagram of the separation method of this invention and the subsequent recovery method. It is a flow chart which shows the procedure of the recovery method of Se alone from Cu _{2 Se.} It is a schematic block diagram of the apparatus used in Example 1. FIG. It is a drawing substitute photograph which shows the state of the MgO crucible after being immersed in molten chloride for 48 hours in Example 1. FIG. It is a drawing substitute photograph which shows the state of the Cu rod after being immersed in molten chloride for 48 hours in Example 1. FIG. 6 is a drawing-substituting photograph showing the contents of the MgO crucible after being immersed in the molten chloride for 48 hours in Example 1. It is a figure which shows the time-dependent change of the electric potential of the electrode and the concentration in salt in Example 1. FIG. It is a figure which shows the cyclic voltammogram measured by the Ni electrode in Example 1. FIG. It is a figure which shows the cyclic voltammogram measured by the Au electrode in Example 1. FIG. It is a figure which shows the XRD pattern of the gray precipitate adhering to the Cu rod in Example 1 and the XRD pattern of the red precipitate which was present at the bottom of the MgO crucible. It is a schematic block diagram of the apparatus used in Example 2. It is a drawing substitute photograph which shows the state of the MgO crucible after being immersed in molten chloride for 48 hours in Example 2. FIG. 2 is a drawing-substituting photograph showing the state of the Ni rod and the contents of the MgO crucible after being immersed in the molten chloride for 48 hours in Example 2. It is a drawing substitute photograph which shows the state of the Ni rod after being immersed in molten chloride for 48 hours in Example 2. FIG. It is a figure which shows the time-dependent change of the concentration in salt in Example 2. It is the schematic of the process of electrolytic reduction treatment of an oxide fuel in molten chloride.

Hereinafter, the configuration of the present invention will be described in detail based on an example of an embodiment shown in the drawings.

1 to 15 show an example of an embodiment of a method for separating selenium and tellurium dissolved in the molten chloride according to the present invention.

In the method for separating selenium and tellurium dissolved in the molten chloride of the present embodiment, a metal oxide (M _x O) composed of the metal M is loaded into the storage container and the metal oxide in the storage container is loaded. And the metal member formed by the metal M is inserted, and the storage container in which the metal member is inserted is immersed in the molten chloride, and selenium (Se) and tellurium (Te) dissolved in the molten chloride. At least one of the above is reacted with a metal oxide to be separated from the molten chloride as a _{metal selenium (M x} Se) or a metal telluride (M _{x Te).}

In the description of the present invention, X as a subscript of M representing a metal does not represent a specific natural number common to all (in other words, a specific value that is the same for all), but each. In each scene where X is used, it is used as an appropriate representation of a voluntary natural number suitable as the X.

<Melted chloride>
The molten chloride to which the present invention is applied is a molten chloride in which at least one of selenium and tellurium is dissolved.

Specific examples of the molten chloride to which the present invention can be applied include molten chloride produced in the electrolytic reduction process of an oxide fuel. Fission products such as selenium and tellurium are dissolved in the molten chloride produced in the electrolytic reduction process of the oxide fuel in the form of anions (that is, Se ^2- and Te ^2-).

In the present invention, at least one of selenium and tellurium dissolved in the molten chloride is separated from the molten chloride.

The composition of the molten chloride itself (that is, the composition of the molten chloride before being subjected to the electrolytic reduction process of the oxide fuel) is, for example, lithium chloride (LiCl) -potassium chloride (KCl) eutectic salt. Calcium chloride (CaCl ₂ ), lithium chloride, potassium chloride, or lithium chloride-potassium chloride eutectic salt, lithium chloride (LiCl), sodium chloride (NaCl) within a range that does not significantly increase the melting point of the molten chloride. ), Potassium chloride (KCl), rubidium chloride (RbCl), cesium chloride (CsCl), calcium chloride (CaCl ₂ ), strontium chloride (SrCl ₂ ), barium chloride (BaCl ₂ ), etc. Examples include those containing more things.

The molten chloride is stored in a reaction vessel and subjected to a separation treatment. The treatment system including the reaction tank is installed in an environment in which an inert gas such as argon (Ar) gas is used as an atmosphere when the separation treatment is performed.

<Metal oxide>
In the present invention, as a metal oxide (M _x O) positioned as an additive, one capable of advancing the following chemical reaction formula (1) when separating selenium from molten chloride is used. Further, when separating tellurium from the molten chloride, one capable of advancing the following chemical reaction formula (2) is used, and further, the molten chloride is formed by _{a single metal oxide (M x O).} When selenium and tellurium are separated from each other at the same time, those capable of advancing the following chemical reaction formulas (1) and (2) are used.
M _x O + Se ^2- → M _x Se + O ^2-・ ・ ・ (1)
M _x O + Te ^2- → M _x Te + O ^2-・ ・ ・ (2)

_{The metal oxide (M x} O) capable of advancing the above chemical reaction formulas (1) and (2) is determined, for example, as follows.

First, the chemical reaction formulas (1) and (2) are rewritten into chemical reaction formulas in consideration of the main components of the molten chloride. For example, when the main component of the molten chloride is lithium chloride (LiCl), the chemical reaction formula (1) is rewritten to the following chemical reaction formula (3), and the chemical reaction formula (2) is changed to the following chemical reaction formula. Rewrite to (4).
M _x O + Li ₂ Se → M _x Se + Li ₂ O ... (3)
M _x O + Li ₂ Te → M _x Te + Li ₂ O ... (4)

_{Next, various metal oxides (M x} O) were used using a known thermodynamic database (specifically, for example, the thermodynamic database "MALT for Windows", Science and Technology, Tokyo, 2004). the chemical reaction formula in the case (3), the standard free energy change (.DELTA.G ⁰⁾ is calculated, and the chemical reaction formula (3), the standard free energy change (.DELTA.G ⁰⁾ (4) less than 0 (4) The metal oxide (M _x O) is a material capable of advancing the chemical reaction formulas (3) and (4).

Here, the metal oxide (M _x O) used in the present invention is composed of a metal M that can be further easily separated from the separated form selenium metal (M _x Se) and tellurized metal (M _{x Te).} It is preferable to make it. As a result, it becomes easy to further separate the metal M from the separated form of the metal selenium (M _x Se) or the metal tellurium (M _x Te) and finally recover it as a simple substance of selenium or a simple substance of tellurium.

Selenium and tellurium are elements that are recovered as by-products in the process of smelting ores (specifically, ores containing copper, lead, and nickel). Therefore, a technique for separating the metal M from the metal selenium (M _x Se) or the metal tellurium (M _x Te) to recover the elemental selenium or the simple substance tellurium has been widely established.

In the present invention, for example, by utilizing the above-mentioned known techniques, the metal M is composed of a metal M that can be further easily separated from _{the separated form selenium metal (M x} Se) and tellurized metal (M _{x Te).} It is preferred that the metal oxide (M _{x O) be selected.}

_{According to the study of the present inventor, copper oxide (Cu 2} O) and nickel oxide (Ni O) are suitable for use in the present invention as metal oxides (M _x O), specifically, for example, as an example. ).

<Contact mode between molten chloride and metal oxide>
A metal oxide is loaded into a storage container configured so that molten chloride can enter through an opening of a part of the container (specifically, for example, the upper part and the upper surface), and the bottom of the storage container is stored. With the metal member inserted into the metal oxide (in other words, with the metal member inserted into the metal oxide so that a part of the metal member comes into contact with the metal oxide; Separation / recovery of selenium metal and tellurite metal by immersing the storage container in molten chloride and removing the storage container from the molten chloride after a certain period of time. do.

The material of the storage container is limited to a specific material as long as it does not react with the material related to the chemical reaction (specifically, separation treatment, selenium metallization metal or tellurium metal formation treatment) according to the present invention. However, an appropriate material is appropriately selected after considering the heat resistance to the temperature of the molten chloride when the separation treatment is performed.

The form of the storage container is not limited to a specific shape, and the metal member is provided with an opening for accommodating the metal oxide so as to surround it from below and allowing molten chloride to enter, and a metal member to the metal oxide pool. A shape in which the metal member can be inserted (or the metal member is brought into contact with the metal oxide) is appropriately selected. Specifically, the storage container can be formed in a crucible shape, for example, in which the upper surface of the container is open.

The metal member inserted into the metal oxide in the storage container is formed of a metal of the same type as the metal constituting the metal oxide in the storage container. Specifically, for example, when copper oxide (Cu ₂ O) is used as the metal oxide, the metal member is formed of copper (Cu), and when nickel oxide (NiO) is used as the metal oxide. Is formed of nickel (Ni).

The form of the metal member inserted into the metal oxide in the storage container is not limited to a specific form, and various forms are appropriately selected. Specifically, the metal member can be formed in a rod shape, a columnar shape, or a prismatic shape, for example.

For example, the position of the interface between the molten chloride and the atmosphere in the rod-shaped metal member and the peripheral portion thereof may be expanded. In this case, the metal member is prevented from being torn due to the progress of wall thinning due to the reaction at the interface position, and the surface area of the metal involved in the reaction is increased to generate selenium metallized metal or tellurium metalized metal more quickly. It becomes possible to separate it from the molten chloride.

Only one metal member may be inserted into one storage container (in other words, a mass of metal oxide in the storage container), or a plurality of metal members may be inserted. In this case, the surface area of the metal involved in the reaction can be increased to more rapidly produce the selenium metal or tellurium metal and separate them from the molten chloride.

The specific surface area of the metal oxide may be increased to increase the contact area between the metal oxide and the molten chloride. The specific surface area of the metal oxide can be increased, for example, by powdering the metal oxide.

Then, by accommodating the metal oxide powder in the accommodating container (in other words, loading it), the contact area between the metal oxide and the molten chloride is increased and dissolved in the molten chloride. The reaction rate between the selenium or tellurium and the metal oxide can be increased, and the selenium or telluride metal can be produced more rapidly and separated from the molten chloride.

Further, it is preferable to agitate the molten chloride in the reaction vessel (particularly, the molten chloride in the vicinity of the accommodating vessel) or to move the accommodating vessel together with the metal member in the molten chloride.

This prevents the occurrence of bias depending on the location of the concentration of selenium and tellurium in the molten chloride, and does not reduce the reaction efficiency and reaction rate between the selenium and tellurium dissolved in the molten chloride and the metal oxide (separately). In other words, the reaction does not slow down), and the selenium metal or tellurium metal can be produced more rapidly and separated from the molten chloride.

Further, a plurality of storage containers in which the metal oxide is contained and the metal member is inserted may be immersed in the molten chloride. This makes it possible to generate selenium metal and tellurium metal more quickly.

<Recovery of selenium metal and tellurium metal>
The metal is further separated from the metal selenium or tellurium metal separated from the molten chloride by the above-mentioned method, and is recovered as a simple substance of selenium or a simple substance of tellurium.

_{As an example, a method of recovering Se alone from Cu 2} Se, which is a separated form when _{Cu 2} O is used as the metal oxide (M _x O), will be described (FIG. 2).

Cu ₂ Se can be separated as _{volatile SeO 2} by oxidative roasting and converting to oxide. _{The Cu 2} O produced at this time can be recycled. Therefore, the generation of secondary waste can be suppressed. SeO ₂ can be recovered as a simple substance by, for example, capturing it in an aqueous solution _{and precipitating Se using a reducing gas (specifically, SO 2 or the like).} Such a method is an established technique in the fields of copper refining and lead refining.

The method for recovering elemental selenium or elemental tellurium from the metallized selenium or tellurium metal separated according to the present invention is not limited to the above-mentioned method, and various methods can be appropriately adopted.

Although the above-described embodiment is an example of a suitable embodiment for carrying out the present invention, the embodiment of the present invention is not limited to the above-mentioned one, and the present invention is not limited to the above-mentioned embodiment. Various modifications can be performed.

For example, in the above-described embodiment, the combination of Cu ₂ O and Cu and the combination of Ni O and Ni are mentioned as the combination of the metal oxide and the metal member, but the metal oxide and the metal that can be used in the present invention are mentioned. The combination with the member is not limited to those listed in the above-described embodiment.

Examples of the present invention will be described below, but the present invention is not limited to the configurations in these examples.

Lithium chloride (LiCl) -potassium chloride (KCl) eutectic salt is used as the molten chloride, and copper oxide (Cu ₂ O) is used as the metal oxide, and selenium (Se) is efficiently separated from the salt by a chemical reaction. It was verified that it could be done.

Specifically, in this embodiment, copper oxide (Cu ₂ O) as a metal oxide composed of copper (Cu) is loaded into a storage container and formed by copper into copper oxide in the storage container. The rod member to be used is inserted, and the storage container in which the rod member is inserted is immersed in a lithium chloride (LiCl) -potassium chloride (KCl) eutectic salt, and selenium (Se) dissolved in the eutectic salt is dissolved. ) Was reacted with copper oxide to be separated from the eutectic salt as a selenium metal (Cu _{2 Se).}

Se dissolves in the molten chloride as an anion such as ^{Se 2-.} In this example, it was intended to separate Se dissolved as ^{Se 2-} ion in salt as a selenium product by reaction with _{Cu 2 O.}

In this example, a crucible with an upper surface opening (referred to as "MgO crucible") made of magnesium oxide (MgO) was used as the storage container.

Then, Cu ₂ O powder was loaded into the Mg O crucible.

In this embodiment, a rod member (referred to as "Cu rod") made of copper (Cu) was also used as the metal member.

Then, the Cu rod was inserted into _{the Cu 2} O powder in the bottom pooled state in the MgO crucible.

Then, the MgO crucible with the Cu rod inserted into _{the Cu 2} O powder in the bottom pool state was immersed in a LiCl-KCl eutectic salt containing ^{Se 2- ions (Fig. 3), 48.} Taken out after hours.

The LiCl-KCl eutectic salt containing ^{Se 2-} ion is a crucible made of _{aluminum oxide (Al 2} O _{3 ) as a reaction vessel (called "Al 2} O ₃ crucible"; inner diameter 48 mm, Nikkato SSA-S. , Al ₂ O ₃ purity 99.6%).

Here, in each figure, reference numeral 1 is an Al ₂ O ₃ crucible (reaction tank), reference numeral 2 is a LiCl-KCl eutectic salt (molten chloride), reference numeral 3 is an MgO crucible (containment vessel), and reference numeral 4 is Cu _2. O powder (metal oxide) and reference numeral 5 represent Cu rods (metal members), respectively. In each figure, reference numeral 6 is a gold (Au) wire having a diameter of 0.5 mm for suspending the MgO crucible.

The details of the test were as follows.
LiCl-KCl eutectic salt: 70.42 g, Se concentration 0.133 wt%, 450 ° C.
Cu ₂ O powder: 0.574 g (containing 3.4 times the equivalent of O relative to the amount of Se in the salt)
Cu rod: Cylindrical MgO crucible with a diameter of 2 mm: Outer diameter 10 mm x inner diameter 8 mm x height 12 mm, Nikkato MG-12G

_{The Al 2} O ₃ crucible 1 as a reaction vessel containing the MgO crucible 3 as a container to be immersed in the LiCl-KCl eutectic salt was installed in an environment in which an argon (Ar) gas was used as an atmosphere.

In order to collect various data related to chemical reactions and control the temperature of LiCl-KCl eutectic salt, the LiCl-KCl eutectic salt in the _{Al 2} O _{3 pot is not shown, but is partially closed Pyrex.} Ag / AgCl reference electrode having a structure in which a LiCl-KCl eutectic salt containing 1.0 wt% silver chloride (AgCl) is placed in a glass tube and a silver (Ag) wire (diameter 1 mm) is inserted, and a gold (Au) wire. (1 mm diameter), nickel (Ni) wire (1 mm diameter), and K thermocouples housed in an _{Al 2} O _{3 protective tube were arranged.}

In the test, salt samples for concentration measurement were also collected 1,2.5, 5, 8, 24, 32, and 48 hours after the MgO pot and Cu rod were immersed, and the Se concentration and Se concentration and The Cu concentration was analyzed and measured by inductively coupled plasma emission spectroscopy (denoted as "ICP-AES").

As a result of the test, it was confirmed that a large amount of gray precipitate was attached around the position above the MgO crucible in the Cu rod (Fig. 4). When this gray precipitate was peeled off, it was confirmed that the Cu rod was thinned (Fig. 5). From this, it was confirmed that the reaction involving the Cu rod proceeded.

When the contents of the crucible were taken out by crushing the MgO crucible, it was confirmed that a red precipitate presumed to be _{Cu 2 O was present at the bottom (Fig. 6).}

It was confirmed that the salt sample collected for the concentration measurement was colored cream with the lapse of the immersion time of the MgO crucible and the Cu rod.

As the _{potential of the Cu 2} O / Cu electrode (which _{means the Cu 2} O powder and the Cu rod in the MgO pot) and the potential of the Au electrode, and the changes in the Se concentration and Cu concentration in the salt over time. The results shown in FIG. 7 were obtained.

From the results shown in FIG. 7, it was confirmed that the Se concentration in the salt (marked with ● in the figure) decreased linearly immediately after the immersion of the MgO crucible and the Cu rod, and decreased to less than 0.01 wt% after 20 hours. A tendency to decrease was confirmed. The analytical value of the Se concentration after 48 hours was 0.0034 wt%, and the Se separation / recovery rate was 97.4%.

Further, _{the potential of the Cu 2} O / Cu electrode and the potential of the Au electrode follow the above-mentioned change in the Se concentration, and change significantly around 18 hours. Therefore, at this point, Se is almost out of the salt. It is suggested that they were separated.

Further, it was confirmed that the Cu concentration in the salt (marked with ▲ in the figure) gradually increased from the time when the above Se was substantially separated from the salt.

FIG. 8 shows a potential-current curve (cyclic voltamogram; referred to as “CV”) measured by the Ni electrode, which was measured before and 48 hours after the MgO crucible and the Cu rod were immersed. The results were obtained, and the results shown in FIG. 9 were obtained as the CV measured by the Au electrode.

From the results shown in FIGS. 8 and 9, it was confirmed that after 48 hours, the current peak related to Se disappeared, while the rise of the anode current was observed from −0.4 V. This is because it coincides with the potential at which the metallic Cu dissolves, so the Cu ⁺ ions in the salt were reduced and the metallic Cu was deposited on the electrode while the potential was scanned toward the cathode side. It was considered that it was considered to be consistent with the result of analysis of Cu concentration by ICP-AES.

However, the reduction current of ^{Cu + ions is small.} Therefore, _{avoid excessive addition of Cu 2 O as much as possible, and pull up the Cu 2} O / Cu electrode (that is, the Cu ₂ O powder and the Cu rod in the Mg O pot) when the Se concentration in the salt drops to some extent. As a result, Cu elution into the salt can be suppressed.

The gray precipitate (Fig. 4) adhering to the Cu rod and the red precipitate (Fig. 6) present at the bottom of the MgO crucible were collected and analyzed by XRD (X-ray diffraction method). The results shown in 10 were obtained.

From the results shown in FIG. 10, _{it was confirmed that the gray precipitate was a mixture of Cu 2} Se and LiCl-KCl, and the salt content was large from the peak intensity.

On the other hand, a red precipitate _LiCuO, it was confirmed that a mixture of Cu 2 O, Cu, and LiCl-KCl.

Metal Cu is considered to have been produced by local electrochemical reactions, specifically, Cu rod part Cu 2 _O in contact with the Cu 2 _O emits O ^2- ions (the following chemical _{At the same time as the reaction formula (6)), Cu 2} Se was generated on the surface of the Cu rod (in other words, the portion where the Cu rod is exposed to the eutectic salt) (the following chemical reaction formula (7)). it was thought.
_{Cu 2 O: Cu 2 O +} 2e - → 2Cu + O 2- ··· (5)
Cu _{^{bars: 2Cu + Se 2- → Cu 2}} Se + 2e - ··· (6)

The electrons are transported along the Cu rod, which is a conductor.

The fact that the reactions of the above chemical reaction formula (6) and the chemical reaction formula (7) proceed respectively is supported by the fact that the Cu rod is thinned in FIG. 5, and the Cu rod is effective as a reaction field. It was confirmed that it was working.

Further, with the formation of LiCuO, Cu ⁺ ions are dissolved in the salt by the following chemical reaction formula (8).
Cu ₂ O + Li ⁺ → Cu ⁺ + LiCuO ・ ・ ・ (7)

From the above results, as a result of _{constructing an electrode (Cu 2} O / Cu electrode) having a structure in which a Cu rod is inserted into _{Cu 2} O powder loaded in an Mg O pot and immersing it in a LiCl-KCl eutectic salt, Cu ₂ O _{Cu 2} Se is also separated around the Cu rod in addition to the interface between the powder and the eutectic ^{salt, reducing the Se 2-} concentration in the salt from 0.133 wt% to 0.0034 wt% (ie, Se separation rate 97). It was confirmed that it is possible to achieve 0.4%).

Further, the above-mentioned reaction behavior confirmed for Se (Se ^2- ion) is considered to be the same for tellurium (Te), which is an element of the same family as Se and has similar chemical properties. rice field.

Further, when the Cu ₂ O powder is simply put in the pot and immersed in the _{molten chloride, the interface between the Cu 2} O powder and the molten chloride (in other words, _{the upper layer surface of the Cu 2} O powder in the pot). The reaction only occurs by itself, but the surface of the Cu rod exposed in the molten chloride also acts as a reaction surface by inserting the Cu rod into the pool _{of Cu 2 O powder in the pot.} It is possible to efficiently proceed the reaction to promote the separation of Se, and in the molten chloride without dispersing / dissipating _{the raw material Cu 2} O powder and the product (that is, Cu _{2 Se).} It was confirmed that it is possible to efficiently separate Se from.

Using calcium chloride (CaCl ₂ ) as the molten chloride and nickel oxide (NiO) as the metal oxide, it was verified that selenium (Se) can be efficiently separated from the salt by a chemical reaction.

Specifically, in this embodiment, nickel oxide (NiO) as a metal oxide composed of nickel (Ni) is loaded into a storage container, and nickel oxide is formed into nickel oxide in the storage container. A rod member is inserted, and the storage container in which the rod member is inserted _{is immersed in calcium chloride (CaCl 2} ), and selenium (Se) dissolved in the calcium chloride is reacted with nickel oxide to cause a metal selenium. It was separated from the calcium chloride as (Ni ₃ Se _2).

In this example, ^{it was intended to separate Se dissolved as Se 2-} ion in salt as a selenium product by reaction with NiO.

In this example, a crucible with an upper surface opening (referred to as "MgO crucible") made of magnesium oxide (MgO) was used as the storage container.

Then, NiO powder was loaded into the MgO crucible.

In this embodiment, a rod member (referred to as "Ni rod") made of nickel (Ni) was also used as the metal member.

Then, the Ni rod was inserted into the NiO powder in the bottom-reservoir state in the MgO crucible.

Then, the MgO crucible in which the Ni rod was still inserted into the NiO powder in the bottom-reservoir state was immersed in CaCl ₂ ^{containing Se 2-} ions (FIG. 11), and was taken out after 48 hours.

_{CaCl 2} containing Se ^2- ion is stored in a crucible made of magnesium oxide (MgO) (called "MgO crucible"; inner diameter 48 mm, Nikkato MG-12G, MgO purity 99.6%) as a reaction vessel. Was done.

Here, in each figure, reference numeral 11 is an MgO crucible (reaction tank), reference numeral 12 is CaCl ₂ (molten chloride), reference numeral 13 is an MgO crucible (containment vessel), and reference numeral 14 is NiO powder (metal oxide). Reference numeral 15 represents a Ni rod (metal member), respectively. In each figure, reference numeral 16 is a gold (Au) wire having a diameter of 0.5 mm for suspending the MgO crucible.

The details of the test were as follows.
CaCl ₂ : 75.322 g, Se concentration 0.100 wt%, 820 ° C.
NiO powder: 0.265 g (including 3.7 times the equivalent of O in salt)
Ni rod: Cylindrical MgO crucible with a diameter of 2 mm: Outer diameter 10 mm x inner diameter 8 mm x height 12 mm, Nikkato MG-12G

The MgO crucible 11 as a reaction vessel containing the MgO crucible 13 as a storage container immersed in CaCl _{2 was installed in an environment in which an argon (Ar) gas was used as an atmosphere.}

In the test, salt samples for concentration measurement were collected 1,2.5, 5, 8, 20, 30, and 48 hours after the MgO crucible and Ni rod were immersed, and the Se concentration and Ni concentration were taken. Was analyzed and measured by inductively coupled plasma emission spectroscopy.

As a result of the test, it was confirmed that the Ni rod was torn at the position above the MgO crucible (in addition, _{the position of the interface between CaCl 2} and the atmosphere) as a result of the progress of wall thinning (FIG. 12). ). From this, it was confirmed that the reaction involving the Ni rod proceeded.

When the contents of the crucible were taken out by crushing the MgO crucible, it was confirmed that a green precipitate was present at the bottom (FIG. 13).

When the contents of the crucible were crushed, the tip (in other words, the lower end) of the Ni rod inserted into the pool of NiO powder in the crucible had a spherical shape presumed to be _{Ni 3} Se _2. It was confirmed that a precipitate was formed (FIGS. 13 and 14).

This is because Ni ₃ Se ₂ is a liquid (that is, a liquid Ni-Se alloy) at 820 ° C. _{Therefore, Ni 3} Se ₂ produced by a chemical reaction travels along the surface of the Ni rod and of the Ni rod in the MgO crucible. It was considered that the lower end (in other words, the bottom of the crucible) formed a spherical shape and accumulated, and after the reaction treatment, it was cooled and solidified while forming a spherical shape. It should be noted that the process of gathering and solidifying while forming droplets is preferable in that the recovery of Ni ₃ Se _{2 from CaCl 2 can be facilitated.}

The results shown in FIG. 15 were obtained as changes in the Se concentration in the salt over time.

From the results shown in FIG. 15, it was confirmed that the Se concentration in the salt decreased linearly from immediately after the immersion of the MgO crucible and the Ni rod to about 20 hours later. The analytical value of the Se concentration after 48 hours was 0.0055 wt%, and the Se separation / recovery rate was 94.6%.

The analytical value of the Ni concentration after 48 hours was 0.0014 wt%. From this _{, it was confirmed that NiO is sparingly soluble in relation to CaCl 2, and therefore, when CaCl 2} is used as the molten chloride, it is confirmed that it is appropriate to use a Ni rod as the metal member. Was done. Incidentally, considered Cu 2 _O is because it is assumed that dissolves readily into CaCl _2, examples of the metal member when the CaCl ₂ is used as the molten chloride is more appropriate for Ni rods than Cu rod Be done.

From the above results, the results immersed in CaCl ₂ to constitute an electrode of a structure of inserting the Ni bar NiO powder and loaded onto a MgO crucible (NiO / Ni electrode), in addition to the interface between the NiO powder and CaCl _{2 Ni 3} Se ₂ is also separated around the Ni rod, and ^{it is possible to reduce the Se 2-} concentration in the salt from 0.100 wt% to 0.0055 wt% (that is, achieve a Se separation rate of 94.6%). It was confirmed that.

Further, the above-mentioned reaction behavior confirmed for Se (Se ^2- ion) is considered to be the same for tellurium (Te), which is an element of the same family as Se and has similar chemical properties. rice field.

Further, when the NiO powder is simply put in the crucible and immersed in the molten chloride, the reaction occurs only at the interface between the NiO powder and the molten chloride (in other words, the upper layer surface of the NiO powder in the crucible). On the other hand, by inserting the Ni rod into the pool of NiO powder in the crucible, the surface of the Ni rod exposed in the molten chloride also acts as a reaction surface, so that the reaction can proceed efficiently. It is possible to promote the separation of Se, and the composition is adjusted by supplying Ni from the Ni rod, although Ni needs to be supplied in order to produce _{Ni 3} Se _{2 from NiO.} The reaction can proceed appropriately, and Se can be efficiently separated from the melt chloride without dispersing / dissipating the raw material NiO powder and the product (that is, Ni ₃ Se _2). It was confirmed that it was possible.

1 Reaction tank (Al ₂ O ₃ crucible)
2 Molten salt (LiCl-KCl eutectic salt)
3 Storage container (MgO crucible)
4 Metal oxide (Cu ₂ O powder)
5 Metal member (Cu rod)
6 Gold wire 11 Reaction tank (MgO crucible)
12 Molten salt (CaCl ₂ )
13 Storage container (MgO crucible)
14 Metal oxide (NiO powder)
15 Metal member (Ni rod)
16 gold wire

Claims (6)

Pledged the metallic member formed of Cu to Cu ₂ O in the storage container with loading the Cu ₂ O to container, melting the container in a state in which pledged metal member formed in the Cu immersed in chloride, wherein the at least one can be reacted with the Cu ₂ O selenide metal or metal telluride of selenium dissolved in the molten chlorides (Se) and tellurium (Te) A method for separating selenium and tellurium dissolved in molten chloride, which comprises separating from molten chloride. The method for separating selenium and tellurium dissolved in the molten chloride according to claim 1, wherein the Cu ₂ O is a powder. Pledged metallic member formed said to NiO in Ni of the storage container with loading of NiO into the container, the container in a state in which pledged metallic member formed by the Ni in molten chloride immersion, separated from the said molten chloride as at least one is reacted with the NiO selenide metal or metal telluride of selenium dissolved in the molten chlorides (Se) and tellurium (Te) A method for separating selenium and tellurium dissolved in molten chloride. The method for separating selenium and tellurium dissolved in the molten chloride according to claim 3 , wherein the NiO is a powder. The molten chloride according to any one of claims 1 to 4, wherein at least one of stirring the molten chloride and moving the containing container in the molten chloride is performed. A method for separating selenium and tellurium dissolved in a substance. Separation of selenium and tellurium dissolved in the molten chloride according to any one of claims 1 to 5, wherein the molten chloride is a LiCl-KCl eutectic _{salt or a CaCl 2 molten salt.} Method.

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